Variable compression ratio internal combustion engine

ABSTRACT

A variable compression ratio internal combustion engine comprises a crankshaft and a connecting rod. The connecting rod comprises a connecting rod body, a first hydraulic cylinder, a first hydraulic piston, a second hydraulic cylinder, a second hydraulic piston, a linking member, a hydraulic oil path, and a spool between a first operating position permitting supply of hydraulic oil from the second hydraulic cylinder to the first hydraulic cylinder, and a second operating position permitting supply of hydraulic oil from the first hydraulic cylinder to the second hydraulic. The variable compression ratio internal combustion engine further comprises a biasing member arranged inside the crank pin and biasing the spool so as to selectively switch a position of the spool between the first operating position and the second operating position.

TECHNICAL FIELD

The present invention relates to a variable compression ratio internalcombustion engine which can change a mechanical compression ratio.

BACKGROUND ART

Known in the past has been an internal combustion engine provided with avariable compression ratio mechanism which can change a mechanicalcompression ratio of the internal combustion engine. As such a variablecompression ratio mechanism, various mechanisms have been proposed. Asone among these, one which can change the effective length of aconnecting rod used in the internal combustion engine may be mentioned(for example, PTLs 1 to 3). In this regard, the “effective length of aconnecting rod” means the length between a center of a crank receivingopening which receives a crank pin and a center of a piston pinreceiving opening which receives a piston pin. Therefore, if theeffective length of a connecting rod becomes longer, a combustionchamber volume when the piston is at top dead center of the compressionstroke becomes smaller, and therefore the mechanical compression ratioincreases. On the other hand, if the effective length of a connectingrod becomes shorter, the combustion chamber volume when the piston is attop dead center of the compression stroke becomes larger, and thereforethe mechanical compression ratio falls.

As described in PLTs 1 to 3, as a variable length connecting rod able tobe changed in its effective length, there is known a connecting rodwhich moves a piston mechanism provided inside a connecting rod byhydraulic oil to change the effective length. In such a variable lengthconnecting rod, to control the position of the piston mechanism and inturn the effective length of the connecting rod, it is necessary tocontrol the flow of hydraulic oil supplied to the piston mechanism.

PLT 1 describes moving the position of a spool arranged in a hydraulicoil path formed inside of a connecting rod body so as to switch thedirection of flow of the hydraulic oil. The spool is switched in itsposition by striking a cam disk arranged inside an oil pan at the timeof rotation of the crankshaft. The position of the cam disk iscontrolled by an electric powered motor arranged inside the oil pan. Bycontrolling the position of the cam disk, the position of the spool isswitched and the effective length of the connecting rod is changed.

CITATION LIST Patent Literature

PLT 1: WO2014/019684A

PLT 2: WO2015/082722A

PLT 3: Japanese Patent Publication No. 2015-527518A

SUMMARY OF INVENTION Technical Problem

However, when arranging additional parts such as a cam disk and anelectric powered motor inside an oil pan, the engine body becomeslarger. It becomes difficult to mount such a variable length connectingrod on an existing internal combustion engine.

Therefore, considering the above problem, an object of the presentinvention is to provide a variable compression ratio internal combustionengine able to keep the engine body from becoming larger while changingthe effective length of the connecting rod.

Solution to Problem

In order to solve the above problem, in a first aspect, there isprovided a variable compression ratio internal combustion enginecomprising a crankshaft and a connecting rod connected to thecrankshaft, wherein the connecting rod comprises a connecting rod bodyprovided with a crank receiving opening receiving a crank pin of thecrankshaft, a first hydraulic cylinder formed at the connecting rod bodyand to which hydraulic oil is supplied, a first hydraulic piston slidinginside the first hydraulic cylinder, a second hydraulic cylinder formedat the connecting rod body and to which hydraulic oil is supplied, asecond hydraulic piston sliding inside the second hydraulic cylinder, alinking member provided with a piston pin receiving opening receiving apiston pin and moving in linkage with the first hydraulic piston and thesecond hydraulic piston so as to change a length between a center of thepiston pin receiving opening and a center of the crank receivingopening, a hydraulic oil path formed inside the connecting rod body andcommunicating with the first hydraulic cylinder and the second hydrauliccylinder, and a spool arranged inside the hydraulic oil path and movingbetween a first operating position prohibiting supply of hydraulic oilthrough the hydraulic oil path from the first hydraulic cylinder to thesecond hydraulic cylinder and permitting supply of hydraulic oil throughthe hydraulic oil path from the second hydraulic cylinder to the firsthydraulic cylinder, and a second operating position permitting supply ofhydraulic oil through the hydraulic oil path from the first hydrauliccylinder to the second hydraulic cylinder and prohibiting supply ofhydraulic oil through the hydraulic oil path from the second hydrauliccylinder to the first hydraulic cylinder, characterized in that thevariable compression ratio internal combustion engine further comprisesa biasing member arranged inside the crank pin and biasing the spool soas to selectively switch a position of the spool between the firstoperating position and the second operating position.

In order to solve the above problem, in a second aspect, there isprovided variable compression ratio internal combustion enginecomprising a crankshaft and a connecting rod connected to thecrankshaft, wherein the connecting rod comprises a connecting rod bodyprovided with a crank receiving opening receiving a crank pin of thecrankshaft, a hydraulic cylinder formed at the connecting rod body andto which hydraulic oil is supplied, a hydraulic piston sliding insidethe hydraulic cylinder, a linking member provided with a piston pinreceiving opening receiving a piston pin and moving in linkage with thehydraulic piston so as to change a length between a center of the pistonpin receiving opening and a center of the crank receiving opening, ahydraulic oil path formed inside the connecting rod body andcommunicating with the hydraulic cylinder, and a spool arranged insidethe hydraulic oil path and moving between a first operating positionpermitting supply of hydraulic oil through the hydraulic oil path to thehydraulic cylinder and prohibiting discharge of hydraulic oil throughthe hydraulic oil path from the hydraulic cylinder, and a secondoperating position prohibiting supply of hydraulic oil through thehydraulic oil path to the hydraulic cylinder and permitting discharge ofhydraulic oil through the hydraulic oil path from the hydrauliccylinder, characterized in that the variable compression ratio internalcombustion engine further comprises a biasing member arranged inside thecrank pin and biasing the spool so as to selectively switch a positionof the spool between the first operating position and the secondoperating position.

In a third aspect, the engine further comprises a biasing spring biasingthe biasing member, and the biasing member is switched by oil pressuresupplied to the biasing member so as to make the biasing spring contractand the biasing force of the biasing spring between a first biasingposition switching the spool to the first operating position and asecond biasing position switching the spool to the second operatingposition, in the first or second aspect.

In a fourth aspect, the biasing member is switched by oil pressuresupplied to one end part of the biasing member and oil pressure suppliedto the other end part of the biasing member between a first biasingposition switching the spool to the first operating position and asecond biasing position switching the spool to the second operatingposition, in the first or second aspect.

In a fifth aspect, the spool moves in parallel with a center axial lineof the crank receiving opening when it moves between the first operatingposition and the second operating position, in any one of the first tofourth aspects.

According to the present invention, there is provided a variablecompression ratio internal combustion engine able to keep the enginebody from becoming larger while changing the effective length of theconnecting rod.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic side cross-sectional view of a variablecompression ratio internal combustion engine according to a firstembodiment.

FIG. 2 is a perspective view schematically showing a variable lengthconnecting rod according to the first embodiment.

FIG. 3 is a side cross-sectional view schematically showing a variablelength connecting rod according to the first embodiment.

FIG. 4 is a schematic disassembled perspective view of the vicinity of asmall diameter end part of a connecting rod body.

FIG. 5 is a schematic partial cross-sectional view of a connecting rodand crankshaft seen from a direction A-A of FIG. 3.

FIG. 6 is a schematic cross-sectional view of a connecting rod andcrankshaft seen from a direction B-B of FIG. 5.

FIG. 7 is a schematic cross-sectional view of a crank pin seen from adirection C-C of FIG. 5.

FIG. 8 is a view similar to FIG. 5 of when the biasing member ispositioned at a second biasing position and a spool is positioned at asecond operating position.

FIG. 9 is a schematic cross-sectional view of a crank pin seen from adirection D-D of FIG. 8.

FIG. 10 is a view schematically showing a hydraulic oil path in thefirst embodiment of the present invention.

FIG. 11 is a view schematically showing a hydraulic oil path in thefirst embodiment of the present invention.

FIG. 12A is a side cross-sectional view schematically showing a variablelength connecting rod according to the first embodiment.

FIG. 12B is a side cross-sectional view schematically showing a variablelength connecting rod according to the first embodiment.

FIG. 13 is a schematic partial cross-sectional view of a connecting rodand crankshaft seen from a direction A-A of FIG. 3.

FIG. 14 is a perspective view schematically showing a variable lengthconnecting rod according to the third embodiment.

FIG. 15 is a side cross-sectional view schematically showing a variablelength connecting rod according to the third embodiment.

FIG. 16 is a view schematically showing a hydraulic oil path in thethird embodiment of the present invention.

FIG. 17 is a view schematically showing a hydraulic oil path in thethird embodiment of the present invention.

FIG. 18A is a side cross-sectional view schematically showing a variablelength connecting rod according to the third embodiment.

FIG. 18B is a side cross-sectional view schematically showing a variablelength connecting rod according to the third embodiment.

DESCRIPTION OF EMBODIMENTS

Below, referring to the drawings, an embodiment of the present inventionwill be explained in detail. Note that, in the following explanation,similar component elements are assigned the same reference notations.

First Embodiment

First, referring to FIGS. 1-12, a variable compression ratio internalcombustion engine according to a first embodiment of the presentinvention will be explained.

<Variable Compression Ratio Internal Combustion Engine>

FIG. 1 is a schematic side cross-sectional view of a variablecompression ratio internal combustion engine according to a firstembodiment. Referring to FIG. 1, 1 shows an internal combustion engine.The internal combustion engine 1 is comprising a crankshaft case 2,cylinder block 3, cylinder head 4, pistons 5, variable length connectingrods 6, combustion chambers 7, spark plugs 8 arranged at the centerparts of top surfaces of the combustion chambers 7, intake valves 9, anintake camshaft 10, intake ports 11, exhaust valves 12, an exhaustcamshaft 13, exhaust ports 14, oil pan 16 and crank shaft 17. Thecylinder block 3 forms cylinders 15. The pistons 5 reciprocate insidethe cylinders 15.

The variable length connecting rod 6 is connected at a small diameterend part thereof by a piston pin 21 to the piston 5, and is connected ata large diameter end part thereof to a crank pin 17 a of the crankshaft17. The variable length connecting rod 6, as explained later, can changethe length from the axis of the piston pin 21 to the axis of the crankpin 17 a, that is, the effective length.

If the effective length of the variable length connecting rod 6 becomeslonger, the length from the crank pin 17 a to the piston pin 21 islonger, and therefore as shown by the solid line in the figure, thevolume of the combustion chamber 7 when the piston 5 is at top deadcenter is smaller. On the other hand, even if the effective length ofthe variable length connecting rod 6 changes, the stroke length of thepiston 5 reciprocating in the cylinder does not change. Therefore, atthis time, the mechanical compression ratio at the internal combustionengine 1 becomes higher.

On the other hand, if the effective length of the variable lengthconnecting rod 6 is shorter, the length from the crank pin 17 a to thepiston pin 21 is shorter, and therefore as shown by the broken line inthe figure, the volume of the combustion chamber when the piston 5 is attop dead center is larger. However, as explained above, the strokelength of the piston 5 is constant. Therefore, at this time, themechanical compression ratio at the internal combustion engine 1 becomeslower.

<Configuration of Variable Length Connecting Rod>

FIG. 2 is a perspective view schematically showing a variable lengthconnecting rod 6 according to a first embodiment, while FIG. 3 is a sidecross-sectional view schematically showing a variable length connectingrod 6 according to a first embodiment. As shown in FIG. 2 and FIG. 3,the variable length connecting rod 6 comprises a connecting rod body 31,an eccentric member 32 attached to the connecting rod body 31 to be ableto swivel, a first hydraulic piston mechanism 33 and a second hydraulicpiston mechanism 34 provided at the connecting rod body 31, a firstconnecting member 45 connecting the eccentric member 32 and the firsthydraulic piston mechanism 33, and a second connecting member 46connecting the eccentric member 32 and the second hydraulic pistonmechanism 34.

<Connecting Rod Body>

First, the connecting rod body 31 will be explained. The connecting rodbody 31 has a large diameter end part 31 a provided with a crankreceiving opening 41 receiving a crank pin 17 a of the crankshaft, asmall diameter end part 31 b provided with a sleeve receiving opening 42receiving a later explained sleeve 32 a of the eccentric member 32, anda rod part 31 c extending between the large diameter end part 31 a andthe small diameter end part 31 b. The large diameter end part 31 a isformed by a cap part 31 d of the connecting rod body 31 being bolted tothe rod part 31 c. The small diameter end part 31 b is arranged at thepiston 5 side and is positioned at the opposite side of the largediameter end part 31 a. Note that, the crank receiving opening 41 islarger than the sleeve receiving opening 42, so the end part of theconnecting rod body 31 at the side where the crank receiving opening 41is provided is called the “large diameter end part 31 a”, while the endpart of the connecting rod body 31 at the side where the sleevereceiving opening 42 is provided is called the “small diameter end part31 b”.

Further, in the present Description, the line X extending between thecenter axis of the crank receiving opening 41 (that is, the axis of thecrankpin 17 a received in the crank receiving opening 41) and the centeraxis of the first sleeve receiving opening 42 (that is, the axis of thesleeve 32 a received in the sleeve receiving opening 42) (FIG. 3), thatis, the line passing through the center of the connecting rod body 31,will be called the “axis X of the connecting rod 6 and connecting rodbody 31”.

Further, the length of the connecting rod 6 in a direction vertical tothe axis X of the connecting rod 6 and vertical to the center axis ofthe crank receiving opening 41 will be called the “width of theconnecting rod 6”. In addition, the length of the connecting rod 6 in adirection parallel to the center axis of the crank receiving opening 41will be called the “thickness of the connecting rod 6”. As will beunderstood from FIG. 2 and FIG. 3, the width of the connecting rod body31 is the smallest at the rod part 31 c between the large diameter endpart 31 a and the small diameter end part 31 b leaving aside the regionwhere the hydraulic piston mechanisms 33 and 34 are provided. Further,the width of the large diameter end part 31 a is larger than the widthof the small diameter end part 31 b. On the other hand, the thickness ofthe connecting rod body 31 is made a substantially constant thicknessleaving aside the region where the hydraulic piston mechanisms 33 and 34are provided.

<Eccentric Member>

Next, the eccentric member 32 will be explained. FIG. 4 is a schematicdisassembled perspective view of the vicinity of the small diameter endpart 31 b of the connecting rod body 31. In FIG. 4, the eccentric member32 is shown in the disassembled state. Referring to FIG. 2 to FIG. 4,the eccentric member 32 is provided with a cylindrical sleeve 32 areceived in the sleeve receiving opening 42 formed in the connecting rodbody 31, a pair of first arms 32 b extending from the sleeve 32 a in onedirection in the width direction of the connecting rod body 31, and apair of second arms 32 c extending from the sleeve 32 a in the otherdirection in the width direction of the connecting rod body 31(substantially opposite direction to above one direction). The sleeve 32a can turn inside the sleeve receiving opening 42. For this reason, theeccentric member 32 is attached at the small diameter end part 31 b ofthe connecting rod 31 to be able to turn with respect to the connectingrod body 31 in the circumferential direction of the small diameter endpart 31 b. The axial line of rotation of the eccentric member 32 matchesthe center axial line of the sleeve receiving opening 42.

Further, at the sleeve 32 a of the eccentric member 32, the piston pinreceiving opening 32 d receiving the piston pin 21 is provided. Thispiston pin receiving opening 32 d is formed in a cylindrical shape. Thecylindrically shaped piston pin receiving opening 32 d is formed so thatits axial line is parallel with the center axial line of the cylindricalouter shape of the sleeve 32 a, but is not coaxial. Therefore, the axialline of the piston pin receiving opening 32 d is offset from the centeraxial line of the cylindrical outer shape of the sleeve 32 a, that is,the axial line of rotation of the eccentric member 32.

In this way, in the present embodiment, the center axial line of thepiston pin receiving opening 32 d is offset from the axial line ofrotation of the eccentric member 32. For this reason, if the eccentricmember 32 rotates, the position of the piston pin receiving opening 32 dinside of the sleeve receiving opening 42 changes. When the position ofthe piston pin receiving opening 32 d is at the large diameter end part31 a side in the sleeve receiving opening 42, the effective length ofthe connecting rod becomes shorter. Conversely, when the position of thepiston pin receiving opening 32 d is at the side opposite to the largediameter end part 31 a side, that is, the small diameter end part 31 bside, in the sleeve receiving opening 42, the effective length of theconnecting rod becomes longer. Therefore, according to this embodiment,the effective length of the connecting rod 6 is changed by making theeccentric member 32 turn. That is, the eccentric member 32 is attachedto the small diameter end part 31 b of the connecting rod body 31 to beable to turn so as to change the effective length of the connecting rod6.

<Hydraulic Piston Mechanism>

Next, referring to FIG. 3, the first hydraulic piston mechanism 33 willbe explained. The first hydraulic piston mechanism 33 has a firsthydraulic cylinder 33 a formed at the rod part 31 c of the connectingrod body 31, a first hydraulic piston 33 b sliding inside the firsthydraulic cylinder 33 a, and a first oil seal 33 c sealing in thehydraulic oil supplied to the inside of the first hydraulic cylinder 33a. The first hydraulic cylinder 33 a is almost entirely or entirelyarranged at the side of the first arm 32 b from the axis X of theconnecting rod 6. Further, the first hydraulic cylinder 33 a extendsslanted by a certain extent of angle with respect to the axis X so as tostick out further to the outside of the connecting rod body 31 in thewidth direction the closer to the small diameter end part 31 b.

The first hydraulic piston 33 b is connected by the first connectingmember 45 to the first arm 32 b of the eccentric member 32. The firsthydraulic piston 33 b is connected by a pin to the first connectingmember 45 to be able to rotate. As shown in FIG. 4, the first arms 32 bof the eccentric member 32 are connected by a pin to the firstconnecting member 45 to be able to rotate at the end part at theopposite side to the side connected to the sleeve 32 a. Therefore, thefirst hydraulic piston 33 b moves in linkage with the eccentric member32. The first oil seal 33 c has a ring shape and is attached to thecircumference of the bottom end part of the first hydraulic piston 33 b.

Next, the second hydraulic piston mechanism 34 will be explained. Thesecond hydraulic piston mechanism 34 has a second hydraulic cylinder 34a formed at a rod part 31 c of the connecting rod body 31, a secondhydraulic piston 34 b sliding inside of the second hydraulic cylinder 34a, and a second oil seal 34 c sealing in the hydraulic oil supplied tothe inside of the second hydraulic cylinder 34 a. The second hydrauliccylinder 34 a is almost entirely or entirely arranged at the second arm32 c side from the axial line X of the connecting rod 6. Further, thesecond hydraulic cylinder 34 a extends slanted by exactly a certainextent of angle from the axial line X so as to project out further tothe outside in the width direction of the connecting rod body 31 thecloser to the small diameter end part 31 b.

The second hydraulic piston 34 b is connected with the second arms 32 cof the eccentric member 32 by the second connecting member 46. Thesecond hydraulic piston 34 b is connected by a pin to the secondconnecting member 46 to be able to rotate. As shown in FIG. 4, thesecond arms 32 c are connected by a pin to the second connecting member46 to be able to rotate at the end part at the opposite side to the sideconnected to the sleeve 32 a. Therefore, the second hydraulic piston 34b moves in linkage with the eccentric member 32. The second oil seal 34c has a ring shape and is attached to the circumference of the bottomend part of the second hydraulic piston 34 b.

<Flow Direction Switching Mechanism>

The variable length connecting rod 6 is further provided with a flowdirection switching mechanism switching the flow of hydraulic oil to thefirst hydraulic piston mechanism 33 and the second hydraulic pistonmechanism 34. The flow direction switching mechanism is provided with ahydraulic oil path 50 through which a hydraulic oil flows, check valves71, 72 and a spool 80 controlling the flow of hydraulic oil, and abiasing member 61 switching the position of the spool 80. As shown inFIG. 3, the hydraulic oil path 50 is formed inside the connecting rodbody 31 and communicates with the first hydraulic cylinder 33 a and thesecond hydraulic cylinder 34 a.

The two check valves 71, 72 and the single spool 80 are arranged in thehydraulic oil path 50 formed inside the connecting rod body 31.Specifically, the two check valves 71, 72 and the spool 80 are arrangedin the axial line direction X of the connecting rod 6 between the crankreceiving opening 41, and the first hydraulic cylinder 33 a and secondhydraulic cylinder 34 a. Further, the check valves 71, 72 are arrangedin the axial line direction X of the connecting rod 6 at the piston pinreceiving opening 32 d side from the spool 80. Further, the check valves71, 72 are arranged at the both sides of the axial line X of theconnecting rod 6, while the spool 80 is arranged on the axial line X ofthe connecting rod 6. Note that, as long as the spool 80 is arranged inthe hydraulic oil path 50 between the two check valves 71, 72, thelayout of the spool 80 and check valves 71, 72 may be different from thelayout shown in FIG. 3.

FIG. 5 is a schematic partial cross-sectional view of a connecting rod 6and crankshaft 17 seen from a direction A-A of FIG. 3. FIG. 6 is aschematic cross-sectional view of a connecting rod 6 and crankshaft 17seen from a direction B-B of FIG. 5. FIG. 7 is a schematiccross-sectional view of a crank pin 17 a seen from a direction C-C ofFIG. 5. Note that, in FIG. 3, the crankshaft 17 is omitted. Further, inFIG. 6, the bottom end part of the connecting rod body 31 including thecap part 31 d is omitted. The crankshaft 17 includes a crank pin 17 a,crank journal 17 b, crank arm 17 c, and counterweight 17 d.

As shown in FIG. 5, the spool 80 is held in a spool holding space 47formed inside the connecting rod body 31. The spool holding space 47 isformed so as to have an axial line extending in parallel with the centeraxial line of the crank receiving opening 41. The spool 80 is insertedfrom one end part of the spool holding space 47. This end part is sealedby a first seal member 81 after insertion of the spool 80.

The spool 80 has a columnar shaped columnar part 80 a and a projectingpart 80 b projecting out from the columnar part 80 a. The projectingpart 80 b projects out in a direction vertical to the axial linedirection of the columnar part 80 a. The projecting part 80 b isarranged in a sliding groove 48 of the spool holding space 47 and slidesinside a sliding groove 48 parallel to the center axial line of thecrank receiving opening 41. The projecting part 80 b of the spool 80 isbiased by the biasing member 61 at the time of rotation of thecrankshaft 17, and thereby the spool 80 moves in parallel with thecenter axial line of the crank receiving opening 41. As shown in FIG. 5to FIG. 7, the crank pin 17 a of the crankshaft 17 is formed with acircumferential direction groove 171 extending in the circumferentialdirection so that at the time of rotation of the crankshaft 17, theprojecting part 80 b will not strike the crank pin 17 a.

The biasing member 61 is arranged inside the crank pin 17 a of thecrankshaft 17. Specifically, the biasing member 61 is held in biasingmember holding space 62 formed inside the crank pin 17 a. Further, thebiasing member holding space 62 also holds a biasing spring 63 biasingthe biasing member 61. The biasing spring 63 is for example a coilspring and biases the biasing member 61 in a direction in parallel tothe center axial line of the crank receiving opening 41.

The biasing member holding space 62 has a cylindrical shape and isformed so that its axial line extends in parallel with the center axialline of the crank receiving opening 41. The biasing member 61 andbiasing spring 63 are inserted from one end part of the biasing memberholding space 62. This end part is sealed by a second seal member 64after insertion of the biasing member 61 and biasing spring 63.

The biasing member 61 has a columnar shape. The biasing member 61 isformed with a switching groove 61 a. The switching groove 61 a extendsin a direction vertical to the axial line direction of the biasingmember 61. As shown in FIG. 7, the switching groove 61 a has a tapershaped first taper wall 61 b and second taper wall 61 c. The width ofthe switching groove 61 a is reduced at the time of rotation of thecrankshaft 17 in the direction in which the projecting part 80 b of thespool 80 passes through the switching groove 61 a (direction of arrow inFIG. 7).

Inside the crankshaft 17, more specifically inside the crank journal 17b and crank arms 17 c of the crankshaft 17, an oil pressure supply path18 for supplying oil pressure to the biasing member 61 is formed. Theoil pressure supply path 18 is communicated with the biasing memberholding space 62 at the end part at the opposite side to the end partwhere the biasing spring 63 is arranged. The oil pressure supply path 18is supplied with oil from an oil pressure supply source (not shown) atthe outside of the crankshaft 17. The oil pressure supplied through theoil pressure supply path 18 to the biasing member 61 acts so as to makethe biasing spring 63 contract.

The magnitude of the oil pressure supplied through the oil pressuresupply path 18 to the biasing member 61 is controlled by an oil pressurecontrol valve (not shown) arranged between the oil pressure supplysource and the oil pressure supply path 18. The biasing member 61 isswitched between a first biasing position and second biasing position bythe oil pressure supplied to the biasing member 61 so as to make thebiasing spring 63 contract and the biasing force of the biasing spring63. The biasing member 61 switches the spool 80 to the first operatingposition at the first biasing position, and switches the spool 80 to thesecond operating position at the second biasing position. The biasingmember 61 moves in parallel with the center axial line of the crankreceiving opening 41 when switched between the first biasing positionand second biasing position.

In FIG. 5, the biasing member 61 is positioned at the first biasingposition, while the spool 80 is positioned at the first operatingposition. When a threshold value or more of oil pressure is supplied tothe biasing member 61, the biasing member 61 moves to the first biasingposition due to contraction of the biasing spring 63 due to the oilpressure. At that time, the biasing member 61 moves against the biasingforce of the biasing spring 63 in parallel with the center axial line ofthe crank receiving opening 41. The threshold value of the oil pressureis determined in accordance with the cross-sectional area of the biasingmember 61 (or cross-sectional area of the biasing member holding space62), the elastic coefficient of the biasing spring 63, etc.

As will be understood from FIG. 7, if the biasing member 61 is switchedfrom the second biasing position to the first biasing position, theprojecting part 80 b of the spool 80 is biased at the time of rotationof the crankshaft 17 by the first taper wall 61 b of the biasing member61. As a result, the spool 80 is switched from the second operatingposition to the first operating position. In the present embodiment, theposition of the spool 80 is switched when the piston 5 passes top deadcenter. Note that the position of the spool 80 may be switched when thepiston 5 passes another position between the top dead center and bottomdead center. For example, the spool 80 may be arranged at the cap part31 d of the connecting rod body 31 and the position of the spool 80 maybe switched when the piston 5 passes bottom dead center.

FIG. 8 is a view similar to FIG. 5 of when the biasing member 61 ispositioned at a second biasing position and a spool 80 is positioned ata second operating position. FIG. 9 is a schematic cross-sectional viewof a crank pin 17 a seen from a direction D-D of FIG. 8. If the biasingmember 61 is not supplied with oil pressure or if the biasing member 61is supplied with less than the threshold value of oil pressure, thebiasing member 61 moves to the second biasing position due to thebiasing force of the biasing spring 63. At this time, the biasing member61 moves in parallel to the center axial line of the crank receivingopening 41 due to the biasing force of the biasing spring 63.

As will be understood from FIG. 9, if the biasing member 61 is switchedfrom the first biasing position to the second biasing position, theprojecting part 80 b of the spool 80 is biased at the time of rotationof the crankshaft 17 by the second taper wall 61 c of the biasing member61. As a result, the spool 80 is switched from the first operatingposition to the second operating position. Therefore, the biasing member61 biases the spool 80 so as to selectively switch the position of thespool 80 between the first operating position and the second operatingposition.

FIG. 10 and FIG. 11 are views schematically showing the hydraulic oilpath 50 in the first embodiment of the present invention. The hydraulicoil path 50 has a first cylinder communicating oil path 51 communicatedwith the first hydraulic cylinder 33 a, and a second cylindercommunicating oil path 52 communicated with the second hydrauliccylinder 34 a. The first cylinder communicating oil path 51 is branchedinto a first communicating oil path 53 and a first space communicatingoil path 54. The second cylinder communicating oil path 52 is branchedinto a second connection oil path 55 and a second space communicatingoil path 56.

The first space communicating oil path 54 communicates with the firstcylinder communicating oil path 51 and the spool holding space 47. Thefirst communicating oil path 53 communicates with a third spacecommunicating oil path 57 communicated with the spool holding space 47and the first cylinder communicating oil path 51. The second spacecommunicating oil path 56 communicates with the second cylindercommunicating oil path 52 and the spool holding space 47. The secondconnection oil path 55 communicates with the third space communicatingoil path 57 and the second cylinder communicating oil path 52.

At the first communicating oil path 53, the first check valve 71 isarranged, while at the second connection oil path 55, the second checkvalve 72 is arranged. The first check valve 71 permits the flow ofhydraulic oil in the first communicating oil path 53 from the spoolholding space 47 to the first hydraulic cylinder 33 a and prohibits theflow of hydraulic oil from the first hydraulic cylinder 33 a to thespool holding space 47. The second check valve 72 permits the flow ofhydraulic oil in the second connection oil path 55 from the spoolholding space 47 to the second hydraulic cylinder 34 a and prohibits theflow of hydraulic oil from the second hydraulic cylinder 34 a to thespool holding space 47.

<Operation of Variable Length Connecting Rod>

Next, referring to FIG. 10 to FIG. 12, the operation of the connectingrod 6 will be explained. FIG. 12A shows the state where the firsthydraulic cylinder 33 a is supplied with hydraulic oil and the secondhydraulic cylinder 34 a is not supplied with hydraulic oil. On the otherhand, FIG. 12B shows the state where the second hydraulic cylinder 34 ais supplied with hydraulic oil and the first hydraulic cylinder 33 a isnot supplied with hydraulic oil.

As explained above, when the biasing member 61 is positioned at thefirst biasing position, the spool 80 is positioned at the firstoperating position. In other words, when the biasing member 61 issupplied with the threshold value or more of oil pressure, the spool 80is positioned at the first operating position. FIG. 10 shows the flow ofhydraulic oil when the spool 80 is positioned at the first operatingposition. At the first position, the spool 80 cuts the communication ofthe first space communicating oil path 54 and the third spacecommunicating oil path 57, and communicates the second spacecommunicating oil path 56 and the third space communicating oil path 57through the spool holding space 47. As a result, the flow of hydraulicoil from the second hydraulic cylinder 34 a to the first hydrauliccylinder 33 a is permitted, while the flow of hydraulic oil from thefirst hydraulic cylinder 33 a to the second hydraulic cylinder 34 a isprohibited. Therefore, at the first operating position, the spool 80prohibits the supply of hydraulic oil through the hydraulic oil path 50from the first hydraulic cylinder 33 a to the second hydraulic cylinder34 a and permits the supply of hydraulic oil through the hydraulic oilpath 50 from the second hydraulic cylinder 34 a to the first hydrauliccylinder 33 a.

In this regard, if the upward inertial force generated by reciprocatingmotion of the piston 5 inside the cylinder 15 of the internal combustionengine 1 acts on the piston pin 21, a downward force acts on the secondhydraulic piston 34 b. If this inertial force is generated after thespool 80 moves to the first operating position, the hydraulic oil insidethe second hydraulic cylinder 34 a is discharged from the secondhydraulic cylinder 34 a. As a result, the hydraulic oil inside thesecond hydraulic cylinder 34 a passes through the second cylindercommunicating oil path 52, the second space communicating oil path 56,the third space communicating oil path 57, the first connection oil path53, and the first cylinder communicating oil path 51, and is supplied tothe first hydraulic cylinder 33 a. For this reason, the first hydraulicpiston 33 b ascends and the second hydraulic piston 34 b descends.

The eccentric member 32 moves in linkage with the first hydraulic piston33 b and the second hydraulic piston 34 b so as to make the effectivelength of the connecting rod 6 change. For this reason, as shown in FIG.12A, the eccentric member 32 is turned in the direction of the arrowmark in the figure, and the piston pin receiving opening 32 d ascends inposition. As a result, the length between the center of the crankreceiving opening 41 and the center of the piston pin receiving opening32 d, that is, the effective length of the connecting rod 6, becomes Llin the figure. Therefore, if using the biasing member 61 to make thespool 80 move to the first operating position, the effective length ofthe connecting rod 6 becomes longer and, in turn, the mechanicalcompression ratio in the internal combustion engine 1 becomes higher.

On the other hand, when the biasing member 61 is positioned at thesecond biasing position, the spool 80 is positioned at the secondoperating position. In other words, when the biasing member 61 issupplied with less than the threshold value of oil pressure or is notsupplied with oil pressure, the spool 80 is positioned at the secondoperating position. FIG. 11 shows the flow of hydraulic oil when thespool 80 is positioned at the second operating position. At the secondposition, the spool 80 communicates the first space communicating oilpath 54 and the third space communicating oil path 57 through the spoolholding space 47 and cuts the communication between the second spacecommunicating oil path 56 and the third space communicating oil path 57.As a result, the flow of hydraulic oil from the first hydraulic cylinder33 a to the second hydraulic cylinder 34 a is permitted, while the flowof hydraulic oil from the second hydraulic cylinder 34 a to the firsthydraulic cylinder 33 a is prohibited. Therefore, at the secondoperating position, the spool 80 prohibits the supply of hydraulic oilthrough the hydraulic oil path 50 from the second hydraulic cylinder 34a to the first hydraulic cylinder 33 a and permits the supply ofhydraulic oil through the hydraulic oil path 50 from the first hydrauliccylinder 33 a to the second hydraulic cylinder 34 a.

In this regard, if the downward inertial force generated byreciprocating motion of the piston 5 inside the cylinder 15 of theinternal combustion engine 1 and the downward explosive force generatedby combustion of the air-fuel mixture inside the combustion chamber 7act on the piston pin 21, a downward force acts on the first hydraulicpiston 33 b. If this inertial force and explosive force are generatedafter the spool 80 moves to the second operating position, the hydraulicoil inside the hydraulic cylinder 33 a is discharged from the firsthydraulic cylinder 33 a. As a result, the hydraulic oil inside the firsthydraulic cylinder 33 a passes through the first cylinder communicatingoil path 51, the first connection oil path 53, the third spacecommunicating oil path 57, the second connection oil path 55, and thesecond cylinder communicating oil path 52, and is supplied to the secondhydraulic cylinder 34 a. For this reason, the first hydraulic piston 33b descends and the second hydraulic piston 34 b ascends.

The eccentric member 32 moves in linkage with the first hydraulic piston33 b and the second hydraulic piston 34 b so as to make the effectivelength of the connecting rod 6 change. For this reason, as shown in FIG.12B, the eccentric member 32 is turned in the direction of the arrowmark in the figure (opposite direction to arrow mark of FIG. 12A) andthe piston pin receiving opening 32 d descends in position. As a result,the length between the center of the crank receiving opening 41 and thecenter of the piston pin receiving opening 32 d, that is, the effectivelength of the connecting rod 6, becomes L2 shorter than L1 in thefigure. Therefore, if using the biasing member 61 to make the spool 80move to the second operating position, the effective length of theconnecting rod 6 becomes shorter and, in turn, the mechanicalcompression ratio in the internal combustion engine 1 becomes lower.

In the present embodiment, as explained above, by using the biasingmember 61 to switch the position of the spool 80 between the firstoperating position and the second operating position, it is possible toswitch the effective length of the connecting rod 6 between L1 and L2.As a result, in the internal combustion engine 1 provided with theconnecting rod 6, the mechanical compression ratio can be changed.

Action and Effect in First Embodiment

In the present embodiment, as explained above, the biasing member 61switching the position of the spool 80 is arranged inside the crank pin17 a of the crankshaft 17. For this reason, the engine body (partcomprised of cylinder head 4, cylinder block 3, crankcase 2, and oil pan16) is kept from becoming larger while the effective length of theconnecting rod 6 can be changed. Further, there is no need to supply oilpressure for controlling the biasing member 61 to the connecting rodbody 31, so it is possible to shorten the oil pressure supply path andpossible to improve the response when switching the mechanicalcompression ratio of the internal combustion engine 1.

In this regard, the inertial force generated by reciprocating motion ofthe piston 5 inside the cylinder 15 of the internal combustion engine 1and the explosive force generated by combustion of the air-fuel mixtureinside a combustion chamber 7 basically act in the vertical direction tothe center axial line of the crank receiving opening 41. As opposed tothis, in the present embodiment, the spool 80 moves parallel to thecenter axial line of the crank receiving opening 41 when moving betweenthe first operating position and the second operating position. For thisreason, in the present embodiment, almost no inertial force andexplosive force act in the operating direction of the spool 80, so it ispossible to suppress mistaken operation of the spool 80 due to inertialforce and explosive force.

Note that, in the present embodiment, the eccentric member 32corresponds to the linking member moving in linkage with the firsthydraulic piston 33 b and the second hydraulic piston 34 b so as tochange the effective length of the connecting rod 6.

<Second Embodiment>Next, a variable compression ratio internalcombustion engine according to the second embodiment of the presentinvention will be explained. The configuration and operation of thevariable compression ratio internal combustion engine according to thesecond embodiment are basically similar to the configuration andoperation of the variable compression ratio internal combustion engineaccording to the first embodiment except for the points explained below.

The variable length connecting rod in the first embodiment is the sameas the variable length connecting rod in the second embodiment. FIG. 13is a schematic partial cross-sectional view of a connecting rod 6 andcrankshaft 17′ seen from a direction A-A of FIG. 3. Note that, in FIG.3, the crankshaft 17′ is omitted. In the second embodiment, the biasingmember 61 is switched between the first biasing position switching thespool 80 to the first operating position and the second biasing positionswitching the spool 80 to the second operating position by the oilpressure supplied to one end part of the biasing member 61 and the oilpressure supplied to the other end part of the biasing member 61. Due tothis, at the time of a low temperature where the oil is high inviscosity, it is possible to improve the response when switching theposition of the spool 80 and in turn the response when switching themechanical compression ratio of the internal combustion engine 1.

Inside the crankshaft 17′, more specifically inside the crank journal 17b and crank arm 17 c of the crankshaft 17′, a first oil pressure supplypath 18 a for supplying oil pressure to one end part of the biasingmember 61 and a second oil pressure supply path 18 b for supplying oilpressure to the other end part of the biasing member 61 are formed. Thefirst oil pressure supply path 18 a is communicated with the biasingmember holding space 62 at one end part of the biasing member holdingspace 62. The second oil pressure supply path 18 b is communicated withthe biasing member holding space 62 at the other end part of the biasingmember holding space 62. The first oil pressure supply path 18 a and thesecond oil pressure supply path 18 b are supplied with oil from an oilpressure supply source (not shown) at the outside of the crankshaft 17′.

The magnitude of the oil pressure supplied through the first oilpressure supply path 18 a to one end part of the biasing member 61 iscontrolled by a first oil pressure control valve (not shown) arrangedbetween the oil pressure supply source and the first oil pressure supplypath 18 a. The magnitude of the oil pressure supplied through the secondoil pressure supply path 18 b to the other end part of the biasingmember 61 is controlled by a second oil pressure control valve (notshown) arranged between the oil pressure supply source and the secondoil pressure supply path 18 b.

If making the oil pressure supplied through the first oil pressuresupply path 18 a to one end part of the biasing member 61 larger thanthe oil pressure supplied through the second oil pressure supply path 18b to the other end part of the biasing member 61, the biasing member 61is switched to the first biasing position. As a result, the spool 80 isswitched to the first operating position. On the other hand, if makingthe oil pressure supplied through the first oil pressure supply path 18a to one end part of the biasing member 61 smaller than the oil pressuresupplied through the second oil pressure supply path 18 b to the otherend part of the biasing member 61, the biasing member 61 is switched tothe second biasing position. As a result, the spool 80 is switched tothe second operating position.

Third Embodiment

Next, a variable compression ratio internal combustion engine accordingto a third embodiment of the present invention will be explained. Theconfiguration and operation of the variable compression ratio internalcombustion engine according to the third embodiment are basicallysimilar to the configuration and operation of the variable compressionratio internal combustion engine according to the first embodimentexcept for the points explained below.

FIG. 14 is a perspective view schematically showing a variable lengthconnecting rod 6′ according to the third embodiment. FIG. 15 is a sidecross-sectional view schematically showing a variable length connectingrod 6′ according to the third embodiment. In the third embodiment, thevariable length connecting rod 6′ is provided with a connecting rod body31, an eccentric member 32 attached to the connecting rod body 31 to beable to rotate, a hydraulic piston mechanism 33′ provided at theconnecting rod body 31, and a connecting member 45′ connecting theeccentric member 32 and the hydraulic piston mechanism 33′. Unlike thefirst embodiment, the variable length connecting rod 6′ is provided witha single hydraulic piston mechanism 33′ and a single connecting member45′.

The hydraulic piston mechanism 33′ has a hydraulic cylinder 33 a′ formedat a rod part 31 c of the connecting rod body 31, a hydraulic piston 33b′ sliding inside of the hydraulic cylinder 33 a′, and an oil seal 33 c′sealing in the hydraulic oil supplied to the inside of the hydrauliccylinder 33 a′. The hydraulic cylinder 33 a′ is almost entirely orentirely arranged at the first arm 32 b side from the axial line X ofthe connecting rod 6′. Further, the hydraulic cylinder 33 a′ extendsslanted by exactly a certain extent of angle from the axial line X so asto project out further to the outside in the width direction of theconnecting rod body 31 the closer to the small diameter end part 31 b.

Further, the variable length connecting rod 6′ is further provided witha flow direction switching mechanism switching the flow of hydraulic oilto the hydraulic piston mechanism 33′. The flow direction switchingmechanism is provided with a hydraulic oil path 50′ through which thehydraulic oil flows, a check valve 73 and spool 80 controlling the flowof hydraulic oil, and a biasing member 61 switching the position of thespool 80. The hydraulic oil path 50′ is formed at the inside of theconnecting rod body 31. Unlike the first embodiment, the variable lengthconnecting rod 6′ is provided with a single check valve 73 and a singlespool 80

The check valve 73 is arranged at the piston pin receiving opening 32 dside from the spool 80 in the axial line direction X of the connectingrod 6. Further, the check valve 73 and the spool 80 is arranged on theaxial line X of the connecting rod 6′. Note that, the layout of thespool 80 and check valve 73 may differ from the layout shown in FIG. 15so long as the check valve 73 is arranged at the hydraulic oil path 50between the hydraulic cylinder 33 a′ and the spool 80. The spool 80 isselectively switched between a first operating position and a secondoperating position by biasing member 61 arranged in the crank pin 17 aof the crankshaft 17 in the same way as the first embodiment.

FIG. 16 and FIG. 17 are views schematically showing the hydraulic oilpath 50′ in a third embodiment of the present invention. The hydraulicoil path 50′ has a cylinder communicating oil path 91 communicated withthe hydraulic cylinder 33 a′, a hydraulic oil supply path 92 supplyinghydraulic oil from the oil supply device 70, and a discharge path 93communicating with the outside of the connecting rod body 31. Thecylinder communicating oil path 91 is branched into a fourth spacecommunicating oil path 94 and a fifth space communicating oil path 95.The hydraulic oil is supplied through the path inside the crankshaft 17from the oil supply device 70 to the hydraulic oil supply path 92.

The fourth space communicating oil path 94 and the fifth spacecommunicating oil path 95 are respectively communicated with thecylinder communicating oil path 91 and spool holding space 47. At thefourth space communicating oil path 94, a check valve 73 is arranged.The check valve 73 permits the flow of hydraulic oil to the hydrauliccylinder 33 a′ from the spool holding space 47 at the fourth spacecommunicating oil path 94 and prohibits the flow of hydraulic oil fromthe hydraulic cylinder 33 a′ to the spool holding space 47.

<Operation of Variable Length Connecting Rod>Next, referring to FIG. 16to FIGS. 18A and 18B, the operation of the connecting rod 6′ will beexplained. FIG. 18A shows the state where the hydraulic cylinder 33 a′is supplied with hydraulic oil. On the other hand, FIG. 18B shows thestate where the hydraulic cylinder 33 a′ is not supplied with hydraulicoil.

In the same way as in the first embodiment, when the biasing member 61is positioned at the first biasing position, the spool 80 is positionedat the first operating position. In other words, when the biasing member61 is supplied with the threshold value or more of oil pressure, thespool 80 is positioned at the first operating position. FIG. 16 showsthe flow of hydraulic oil when the spool 80 is positioned at the firstoperating position. At the first operating position, the spool 80 cutsthe communication between the fifth space communicating oil path 95 andthe discharge path 93, and communicates the hydraulic oil supply path 92and the fourth space communicating oil path 94 through the spool holdingspace 47. As a result, the supply of hydraulic oil to the hydrauliccylinder 33 a′ is permitted and the discharge of hydraulic oil from thehydraulic cylinder 33 a′ is prohibited. Therefore, at the firstoperating position, the spool 80 permits the supply of hydraulic oilthrough the hydraulic oil path 50′ to the hydraulic cylinder 33 a′ andprohibits the discharge of hydraulic oil through the hydraulic oil path50′ from the hydraulic cylinder 33 a′.

The hydraulic oil supplied from the oil supply device 70 passes throughthe hydraulic oil supply path 92, fourth space communicating oil path94, and cylinder communicating oil path 91, and is supplied to thehydraulic cylinder 33 a′. For this reason, the hydraulic piston 33 b′ascends.

The eccentric member 32 moves in linkage with the hydraulic piston 33 b′so as to change the effective length of the connecting rod 6′. For thisreason, as shown in FIG. 18A, the eccentric member 32 is turned in thedirection of the arrow mark in the figure and the piston pin receivingopening 32 d ascends in position. As a result, the length between thecenter of the crank receiving opening 41 and the center of the pistonpin receiving opening 32 d, that is, the effective length of theconnecting rod 6′, becomes longer and becomes L1 in the figure.Therefore, if using the biasing member 61 to move the spool 80 to thefirst operating position, the effective length of the connecting rod 6′becomes longer and, in turn, the mechanical compression ratio at theinternal combustion engine becomes higher.

On the other hand, in the same way as the first embodiment, when thebiasing member 61 is positioned at the second biasing position, thespool 80 is positioned at the second operating position. In other words,when the biasing member 61 is supplied with less than the thresholdvalue of oil pressure or is not supplied with oil pressure, the spool 80is positioned at the second operating position. FIG. 17 shows the flowof hydraulic oil when the spool 80 is positioned at the second operatingposition. At the second position, the spool 80 communicates the fifthspace communicating oil path 95 and the discharge path 93 through thespool holding space 47 and cuts the hydraulic oil supply path 92 andfourth space communicating oil path 94. As a result, the supply ofhydraulic oil to the hydraulic cylinder 33 a′ is prohibited anddischarge of hydraulic oil from the hydraulic cylinder 33 a′ ispermitted. Therefore, at the second operating position, the spool 80prohibits the supply of hydraulic oil through the hydraulic oil path 50′to the hydraulic cylinder 33 a′ and permits the discharge of hydraulicoil through the hydraulic oil path 50′ from the hydraulic cylinder 33a′.

In this regard, if the downward inertial force generated byreciprocating motion of the piston 5 inside the cylinder 15 of theinternal combustion engine 1 and the downward explosive force generatedby combustion of the air-fuel mixture inside a combustion chamber 7 acton the piston pin 21, a downward force acts on the hydraulic piston 33b′. If this inertial force and explosive force are generated after thespool 80 moves to the second operating position, the hydraulic oilinside the hydraulic cylinder 33 a′ is discharged from the hydrauliccylinder 33 a′. As a result, the hydraulic oil inside the hydrauliccylinder 33 a′ passes through the cylinder communicating oil path 91,the fifth space communicating oil path 95, and the discharge path 93,and is discharged to the outside of the connecting rod body 31. For thisreason, the hydraulic piston 33 b′ descends.

The eccentric member 32 moves in linkage with the hydraulic piston 33 b′so as to change the effective length of the connecting rod 6′. For thisreason, as shown in FIG. 18B, the eccentric member 32 is turned in thedirection of the arrow mark in the figure (opposite direction to arrowmark of FIG. 18A) and the piston pin receiving opening 32 d descends inposition. As a result, the length between the center of the crankreceiving opening 41 and the center of the piston pin receiving opening32 d, that is, the effective length of the connecting rod 6′, becomes L2shorter than Ll in the figure. Therefore, if using the biasing member 61to make the spool 80 move to the second operating position, theeffective length of the connecting rod 6′ becomes shorter and, in turn,the mechanical compression ratio at the internal combustion enginebecomes lower.

In the third embodiment, as explained above, it is possible to use thebiasing member 61 to switch the spool 80 between the first operatingposition and the second operating position to thereby switch theeffective length of the connecting rod 6′ between Ll and L2. As aresult, in an internal combustion engine 1 provided with the connectingrod 6′, it is possible to change the mechanical compression ratio.

In the third embodiment, in the same way as the first embodiment, thebiasing member 61 switching the position of the spool 80 are arranged inthe crank pin 17 a of the crankshaft 17. For this reason, it is possibleto keep the engine body from becoming larger while changing theeffective length of the connecting rod 6′. Further, there is no need tosupply oil pressure for controlling the biasing member 61 to theconnecting rod body 31, so it is possible to shorten the oil pressuresupply path and possible to improve the response when switching themechanical compression ratio of the internal combustion engine.

Further, in the third embodiment, unlike the first embodiment, there area single hydraulic piston mechanism and a single connecting member. Forthis reason, the number of parts of the variable length connecting rodcan be reduced. As a result, in the third embodiment, it is possible toreduce the total weight and manufacturing cost of the variable lengthconnecting rod.

Note that, in the third embodiment, the eccentric member 32 correspondsto the linking member moving in linkage with the hydraulic piston 33 b′so as to change the effective length of the connecting rod 6′. However,the linking member may be a member such as described in PLT 3 movinglinearly in the axial line direction of the connecting rod together withthe hydraulic piston.

Other Embodiments

Below, preferred embodiments according to the present invention wereexplained, but the present invention is not limited to theseembodiments. Various modifications and changes may be made within thelanguage of the claims. For example, the direction of movement of thespool 80 by the biasing member 61 may be slanted with respect to thecenter axial line of the crank receiving opening 41. Further, thehydraulic oil paths 50, 50′ in the embodiments may be different from thehydraulic oil paths shown in FIG. 10, FIG. 11, FIG. 16, and FIG. 17 solong as able to switch the flow of hydraulic oil due to movement of thespool 80. For example, in the first embodiment and the secondembodiment, the hydraulic oil path 50 may have a refill path forrefilling new hydraulic oil when hydraulic oil leaks from the hydraulicpiston mechanisms 33, 34 etc. In this case, the refill path is suppliedwith hydraulic oil through a path formed inside the crankshaft 17 froman oil pressure supply source at the outside of the connecting rod body31.

Further, the above embodiments can be carried out in any combinations.For example, in the third embodiment, like in the second embodiment, thebiasing member 61 may be switched between the first biasing positionswitching the spool 80 to the first operating position and the secondbiasing position switching the spool 80 to the second operating positionby the oil pressure supplied to one end part of the biasing member 61and the oil pressure supplied to the other end part of the biasingmember 61.

Note that, in this Description, rise of the hydraulic piston means thatthe hydraulic piston moves so as to approach the small diameter end part31 b of the connecting rod body in the axial direction of the connectingrod, while descent of the hydraulic piston means that the hydraulicpiston moves so as to be away from the small diameter end part in theaxial direction of the connecting rod.

REFERENCE SIGNS LIST

1. internal combustion engine

-   6, 6′. connecting rod-   17. crankshaft-   17 a. crank pin-   21. piston pin-   31. connecting rod body-   32. eccentric member-   32 d. piston pin receiving opening-   33 a. first hydraulic cylinder-   33 b. first hydraulic piston-   34 a. second hydraulic cylinder-   34 b. second hydraulic piston-   33 a′. hydraulic cylinder-   33 b′. hydraulic piston-   41. crank receiving opening-   50, 50′. hydraulic oil path-   61. biasing member-   80. spool

1. A variable compression ratio internal combustion engine comprising acrankshaft and a connecting rod connected to the crankshaft, wherein theconnecting rod comprises a connecting rod body provided with a crankreceiving opening receiving a crank pin of the crankshaft, a firsthydraulic cylinder formed at the connecting rod body and to whichhydraulic oil is supplied, a first hydraulic piston sliding inside thefirst hydraulic cylinder, a second hydraulic cylinder formed at theconnecting rod body and to which hydraulic oil is supplied, a secondhydraulic piston sliding inside the second hydraulic cylinder, a linkingmember provided with a piston pin receiving opening receiving a pistonpin and moving in linkage with the first hydraulic piston and the secondhydraulic piston so as to change a length between a center of the pistonpin receiving opening and a center of the crank receiving opening, ahydraulic oil path formed inside the connecting rod body andcommunicating with the first hydraulic cylinder and the second hydrauliccylinder, and a spool arranged inside the hydraulic oil path and movingbetween a first operating position prohibiting supply of hydraulic oilthrough the hydraulic oil path from the first hydraulic cylinder to thesecond hydraulic cylinder and permitting supply of hydraulic oil throughthe hydraulic oil path from the second hydraulic cylinder to the firsthydraulic cylinder, and a second operating position permitting supply ofhydraulic oil through the hydraulic oil path from the first hydrauliccylinder to the second hydraulic cylinder and prohibiting supply ofhydraulic oil through the hydraulic oil path from the second hydrauliccylinder to the first hydraulic cylinder, characterized in that thevariable compression ratio internal combustion engine further comprisesa biasing member arranged inside the crank pin and biasing the spool soas to selectively switch a position of the spool between the firstoperating position and the second operating position.
 2. A variablecompression ratio internal combustion engine comprising a crankshaft anda connecting rod connected to the crankshaft, wherein the connecting rodcomprises a connecting rod body provided with a crank receiving openingreceiving a crank pin of the crankshaft, a hydraulic cylinder formed atthe connecting rod body and to which hydraulic oil is supplied, ahydraulic piston sliding inside the hydraulic cylinder, a linking memberprovided with a piston pin receiving opening receiving a piston pin andmoving in linkage with the hydraulic piston so as to change a lengthbetween a center of the piston pin receiving opening and a center of thecrank receiving opening, a hydraulic oil path formed inside theconnecting rod body and communicating with the hydraulic cylinder, and aspool arranged inside the hydraulic oil path and moving between a firstoperating position permitting supply of hydraulic oil through thehydraulic oil path to the hydraulic cylinder and prohibiting dischargeof hydraulic oil through the hydraulic oil path from the hydrauliccylinder, and a second operating position prohibiting supply ofhydraulic oil through the hydraulic oil path to the hydraulic cylinderand permitting discharge of hydraulic oil through the hydraulic oil pathfrom the hydraulic cylinder, characterized in that the variablecompression ratio internal combustion engine further comprises a biasingmember arranged inside the crank pin and biasing the spool so as toselectively switch a position of the spool between the first operatingposition and the second operating position.
 3. The variable compressionratio internal combustion engine according to claim 1, wherein theengine further comprises a biasing spring biasing the biasing member,and the biasing member is switched by oil pressure supplied to thebiasing member so as to make the biasing spring contract and the biasingforce of the biasing spring between a first biasing position switchingthe spool to the first operating position and a second biasing positionswitching the spool to the second operating position.
 4. The variablecompression ratio internal combustion engine according to claim 2,wherein the engine further comprises a biasing spring biasing thebiasing member, and the biasing member is switched by oil pressuresupplied to the biasing member so as to make the biasing spring contractand the biasing force of the biasing spring between a first biasingposition switching the spool to the first operating position and asecond biasing position switching the spool to the second operatingposition.
 5. The variable compression ratio internal combustion engineaccording to claim 1, wherein the biasing member is switched by oilpressure supplied to one end part of the biasing member and oil pressuresupplied to the other end part of the biasing member between a firstbiasing position switching the spool to the first operating position anda second biasing position switching the spool to the second operatingposition.
 6. The variable compression ratio internal combustion engineaccording to claim 2, wherein the biasing member is switched by oilpressure supplied to one end part of the biasing member and oil pressuresupplied to the other end part of the biasing member between a firstbiasing position switching the spool to the first operating position anda second biasing position switching the spool to the second operatingposition.
 7. The variable compression ratio internal combustion engineaccording to claim 1, wherein the spool moves in parallel with a centeraxial line of the crank receiving opening when it moves between thefirst operating position and the second operating position.
 8. Thevariable compression ratio internal combustion engine according to claim2, wherein the spool moves in parallel with a center axial line of thecrank receiving opening when it moves between the first operatingposition and the second operating position.
 9. The variable compressionratio internal combustion engine according to claim 3, wherein the spoolmoves in parallel with a center axial line of the crank receivingopening when it moves between the first operating position and thesecond operating position.
 10. The variable compression ratio internalcombustion engine according to claim 4, wherein the spool moves inparallel with a center axial line of the crank receiving opening when itmoves between the first operating position and the second operatingposition.
 11. The variable compression ratio internal combustion engineaccording to claim 5, wherein the spool moves in parallel with a centeraxial line of the crank receiving opening when it moves between thefirst operating position and the second operating position.
 12. Thevariable compression ratio internal combustion engine according to claim6, wherein the spool moves in parallel with a center axial line of thecrank receiving opening when it moves between the first operatingposition and the second operating position.